Remove relying on "encoding/json"

This originally depended on "encoding/json" if no options are passed and
only depended on "github.com/go-json-experiment/v1" if options are passed.

This was a faulty attempt at making it possible to detect
divergences in behavior between the two, but it does not work.

We may need to add explicit API to detect regressions between
"encoding/json" and "github.com/go-json-experiment/json/v1".
However, this is complicated by the fact that they will actually
be the same package once Go 1.25 is released and
the binary is built with GOEXPERIMENT=jsonv2.

Author: dsnet

jsonsplit.go

@@ -133,8 +133,6 @@ import (
 	"time"
 	"unicode"
 
-	jsonv1std "encoding/json"
-
 	jsonv2 "github.com/go-json-experiment/json"            // TODO: Use "encoding/json/v2"
 	jsontext "github.com/go-json-experiment/json/jsontext" // TODO: Use "encoding/json/jsontext"
 	jsonv1 "github.com/go-json-experiment/json/v1"         // TODO: Use "encoding/json"
@@ -443,7 +441,7 @@ const (
 	// CallV2ButUponErrorReturnV1 specifies to call v2 by default,
 	// but only when an error occurs, to call v1 and return its result instead.
 	CallV2ButUponErrorReturnV1
-	// OnlyCallV1 specifies to only call v2 functionality.
+	// OnlyCallV2 specifies to only call v2 functionality.
 	OnlyCallV2
 
 	maxCallMode
@@ -866,7 +864,7 @@ func isPointerToZero(p reflect.Value) bool {
 // but allows specifying options to override default v1 behavior.
 func jsonv1Marshal(v any, o ...jsonv2.Options) ([]byte, error) {
 	if len(o) == 0 {
-		return jsonv1std.Marshal(v)
+		return jsonv1.Marshal(v)
 	}
 	var arr [8]jsonv2.Options
 	return jsonv2.Marshal(v, append(append(arr[:0], jsonv1.DefaultOptionsV1()), o...)...)
@@ -876,7 +874,7 @@ func jsonv1Marshal(v any, o ...jsonv2.Options) ([]byte, error) {
 // but allows specifying options to override default v1 behavior.
 func jsonv1Unmarshal(b []byte, v any, o ...jsonv2.Options) error {
 	if len(o) == 0 {
-		return jsonv1std.Unmarshal(b, v)
+		return jsonv1.Unmarshal(b, v)
 	}
 	var arr [8]jsonv2.Options
 	return jsonv2.Unmarshal(b, v, append(append(arr[:0], jsonv1.DefaultOptionsV1()), o...)...)